The effects of temperature, salinity, and the carbonate system on Mg/Ca in Globigerinoides ruber (white) : a global sediment trap calibration
Abstract
The Mg/Ca of planktic foraminifera Globigerinoides ruber (white) is a widely applied proxy for tropical and sub-tropical sea-surface temperature. The accuracy with which temperature can be reconstructed depends on how accurately relationships between Mg/Ca and temperature and the multiple secondary controls on Mg/Ca are known; however, these relationships remain poorly quantified under oceanic conditions. Here, we present new calibrations based on 440 sediment trap/plankton tow samples from the Atlantic, Pacific and Indian Oceans, including 130 new samples from the Bay of Bengal/Arabian Sea and the tropical Atlantic Ocean. Our results indicate temperature, salinity and the carbonate system all significantly influence Mg/Ca in G. ruber (white). We propose two calibration models: The first model assumes pH is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.0±0.8%/°C (2σ), a salinity sensitivity of 3.3±2.2%/PSU and a pH sensitivity of −8.3±7.7%/0.1 pH units; The second model assumes carbonate ion concentration ([CO32−]) is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.7±0.8%/°C, a salinity sensitivity of 5.0±3.0%/PSU and a [CO32−] sensitivity of −0.24±0.11%/μmol kg−1. In both models, the temperature sensitivity is significantly lower than the widely-applied sensitivity of 9.0±0.6%/°C. Application of our new calibrations to down-core data from the Last Glacial Maximum, considering whole ocean changes in salinity and carbonate chemistry, indicate a cooling of 2.4±1.6°C in the tropical oceans if pH is the controlling parameter and 1.5±1.4°C if [CO32−] is the controlling parameter.
Citation
Gray , W R , Weldeab , S , Lea , D W , Rosenthal , Y , Gruber , N , Donner , B & Fischer , G 2018 , ' The effects of temperature, salinity, and the carbonate system on Mg/Ca in Globigerinoides ruber (white) : a global sediment trap calibration ' , Earth and Planetary Science Letters , vol. 482 , pp. 607-620 . https://doi.org/10.1016/j.epsl.2017.11.026
Publication
Earth and Planetary Science Letters
Status
Peer reviewed
ISSN
0012-821XType
Journal article
Description
This research was funded by NSF grant NSF-OCE 1260696 awarded to S. Weldeab and D.W. Lea.Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.